﻿/*
* Copyright (c) 2006-2007 Erin Catto http://www.gphysics.com
*
* This software is provided 'as-is', without any express or implied
* warranty.  In no event will the authors be held liable for any damages
* arising from the use of this software.
* Permission is granted to anyone to use this software for any purpose,
* including commercial applications, and to alter it and redistribute it
* freely, subject to the following restrictions:
* 1. The origin of this software must not be misrepresented; you must not
* claim that you wrote the original software. If you use this software
* in a product, an acknowledgment in the product documentation would be
* appreciated but is not required.
* 2. Altered source versions must be plainly marked as such, and must not be
* misrepresented as being the original software.
* 3. This notice may not be removed or altered from any source distribution.
*/

package Box2D.Collision{
   
import Box2D.Collision.*;
import Box2D.Common.Math.*;
import Box2D.Common.*;

// A manifold for two touching convex shapes.
public class b2Segment
{
   /// Ray cast against this segment with another segment.
   // Collision Detection in Interactive 3D Environments by Gino van den Bergen
   // From Section 3.4.1
   // x = mu1 * p1 + mu2 * p2
   // mu1 + mu2 = 1 && mu1 >= 0 && mu2 >= 0
   // mu1 = 1 - mu2;
   // x = (1 - mu2) * p1 + mu2 * p2
   //   = p1 + mu2 * (p2 - p1)
   // x = s + a * r (s := start, r := end - start)
   // s + a * r = p1 + mu2 * d (d := p2 - p1)
   // -a * r + mu2 * d = b (b := s - p1)
   // [-r d] * [a; mu2] = b
   // Cramer's rule:
   // denom = det[-r d]
   // a = det[b d] / denom
   // mu2 = det[-r b] / denom
   public function TestSegment(lambda:Array, // float pointer
                        normal:b2Vec2, // pointer
                        segment:b2Segment, 
                        maxLambda:Number) : Boolean{
      //b2Vec2 s = segment.p1;
      var s:b2Vec2 = segment.p1;
      //b2Vec2 r = segment.p2 - s;
      var rX:Number = segment.p2.x - s.x;
      var rY:Number = segment.p2.y - s.y;
      //b2Vec2 d = p2 - p1;
      var dX:Number = p2.x - p1.x;
      var dY:Number = p2.y - p1.y;
      //b2Vec2 n = b2Cross(d, 1.0f);
      var nX:Number = dY;
      var nY:Number = -dX;
      
      var k_slop:Number = 100.0 * Number.MIN_VALUE;
      //var denom:Number = -b2Dot(r, n);
      var denom:Number = -(rX*nX + rY*nY);
      
      // Cull back facing collision and ignore parallel segments.
      if (denom > k_slop)
      {
         // Does the segment intersect the infinite line associated with this segment?
         //b2Vec2 b = s - p1;
         var bX:Number = s.x - p1.x;
         var bY:Number = s.y - p1.y;
         //var a:Number = b2Dot(b, n);
         var a:Number = (bX*nX + bY*nY);
         
         if (0.0 <= a && a <= maxLambda * denom)
         {
            var mu2:Number = -rX * bY + rY * bX;
            
            // Does the segment intersect this segment?
            if (-k_slop * denom <= mu2 && mu2 <= denom * (1.0 + k_slop))
            {
               a /= denom;
               //n.Normalize();
               var nLen:Number = Math.sqrt(nX*nX + nY*nY);
               nX /= nLen;
               nY /= nLen;
               //*lambda = a;
               lambda[0] = a;
               //*normal = n;
               normal.Set(nX, nY);
               return true;
            }
         }
      }
      
      return false;
   }
   
   public var p1:b2Vec2 = new b2Vec2();   ///< the starting point
   public var p2:b2Vec2 = new b2Vec2();   ///< the ending point
};


}